For reasons of economy, some nickel-plated electrical contacts in commercial use have gold platings (over the nickel) that are relatively thin, i.e., 0.1-0.25 .mu.m in thickness. However, such thin gold layers are generally porous, and in order to prevent corrosion and tarnishing, a further protective surface treatment is required. Chromate treatment appears to inhibit corrosion to some extent. However, where the gold overplating is absent or is very thin (i.e., no more than about 0.1 .mu.m thick), chromate treatment alone often provides inadequate surface protection. Practitioners have hitherto been unable to provide a surface treatment that supplements, or replaces, chromate treatment, and that can give adequate protection to treated surfaces without substantially increasing their contact resistance. This application describes such a treatment.